Carriage arm assembly for locating magnetic head, and magnetic disk apparatus using the same

ABSTRACT

A carriage arm assembly for swingably supporting a magnetic head which includes a slider, a suspension carrying the slider, a carriage arm to which the suspension is attached, and a body section. The carriage arm extends from the body section and includes first and second arm members extending substantially in parallel with a swinging plane of the carriage arm, and a fixing portion provided at a distal end of the carriage arm for mounting the suspension thereon. Each of the first and second arm members have narrow sections in a distal end area and a base end area thereof, wherein a width of the narrow sections in a swinging direction is smaller than a width of an intermediate area of the first and second arm members.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.10/157,087, filed May 30, 2002, now U.S. Pat. No. 6,879,467, thecontents of which is incorporated by reference herein, and is copendingwith continuation-in-part application Ser. No. 10/372,833, filed Feb.26, 2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetic disk apparatus, and moreparticularly to a carriage arm assembly used for positioning a magnetichead of the magnetic disk apparatus.

2. Description of the Prior Art

In the field of a magnetic disk apparatus, it has been required toimprove recording density thereof to increase recording capacity. Forthis purpose, it is important to improve accuracy in positioning amagnetic head. However, as obstacles to the improvement of thepositioning accuracy, there are a positioning error due to vibration ofa mechanical system caused by rotating a disk or moving a carriage armassembly, and a positioning error caused when vibration is added fromthe outside of the magnetic disk apparatus. Accordingly, effectivemethods for reducing these positioning errors are to widen a servo bandwidth, and to reduce the vibration caused by the mechanical system.

To widen the servo band width is greatly effected by a primary vibrationmode or a main resonance mode with respect to a transfer characteristicof the carriage arm assembly, in which modes the input is defined as aforce generated in a coil, and the output is defined as a displacementamount of the magnetic head in the positioning direction. This mainresonance mode is the same deformation mode with the “lateral bendingsystem mode” in a document of “Analytical and Experimental Study of theEffect of Base-Plate and Top Cover Stiffness on Actuator and Disk packDynamics” (Yih-Jen Dennis et al., 10th Annual Symposium on InformationStorage and Processing Systems, Jun. 28 to 30, 1999), the “butterflymode” in a document of “Active Damping in HDD Actuator” (Fu-Ying Huanget al., IEEE TRANSACTIONS ON MAGNETICS, VOL. 37, No. 2., March 2001),and the “QR mode” in a document of “Development of a Single Coil CoupledForce VCM Actuator for High TPI Magnetic Recording” (Huai Lin et al.,IEEE TRANSACTIONS ON MAGNETICS, VOL. 37, No. 2., March 2001).

In the case of widening the servo band width, one of restrictions is again margin in a natural frequency of the main resonance mode(hereinafter referred to as “main resonance frequency”). If the mainresonance frequency is low with respect to the servo band width, oramplitude is large, the gain margin is reduced, and in the worst case,the control system becomes oscillated, so that the positioning controlcannot be achieved. In other words, it is possible to secure the gainmargin to widen the servo band width by raising the main resonancefrequency or decreasing the gain in the transfer characteristic. Forexample, JP-A-2000-48497 discloses an example in which the mainresonance frequency is heightened by changing coupling method of abearing of the carriage arm assembly so as to improve the rigidity.Further, JP-A-09-161430 shows an example which is designed so that themagnetic head is not displaced in the main resonance mode, however, theexample has not been applied to an actual apparatus.

On the other hand, the vibration caused by the mechanical system duringthe positioning operation of the carriage arm assembly is mainlygenerated by excitation of each part of the carriage arm assembly due todriving force input to the carriage arm assembly for positioning thehead on a target track during the moving operation from one track toanother track.

Especially, a vibration mode in which in-plane bending of the carriagearm (hereinafter simply referred to as “arm”) is considered is greatlyon the positioning accuracy of the carriage arm assembly because thehead is disposed at an end of the arm and thus is swung around in thecase of an swing type of carriage arm assembly. As this kind ofvibration mode, there are the above-described main resonance mode, andan arm in-plane bending primary mode, for example. In this mainresonance mode, deformation of the bearing section and bendingdeformation of the overall carriage arm assembly are combined. Further,in the arm in-plane bending primary mode, each of a plurality of armsdeforms just like primary bending of a cantilever.

In addition, there is a problem that residual vibration in thepositioning operation increases the time until starting to read/writedata, so that the reading/writing speed of the disk apparatus isreduced. An example of the method of reducing the residual vibration isshown in JP-A-11-66773, which reduces the vibration using a tuned massdamper.

BRIEF SUMMARY OF THE INVENTION

The main resonance mode is a mode in which the deformation of thebearing section and the deformation of the overall carriage arm assemblyare combined. Thus, in order to raise the main resonance frequency, itis effective to increase the overall rigidity of the bearing and thecarriage arm assembly, or reduce the weight of the carriage armassembly. However, in an actual magnetic disk apparatus, it is coming toa critical limit to increase the rigidity of the bearing. Regarding thecarriage arm assembly, the drastic increase of the rigidity and theweight reduction are contradictory to each other, and thus it isdifficult to drastically heighten the main resonance frequency. That is,it is now coming closer to the critical limit to widen the servo bandwidth by raising the main resonance frequency.

In an example shown in JP-A-9-161430, the displacement of the magnetichead is 0 (in the main resonance mode), and thus it is possible todrastically widen the servo band width in the sense that the mainresonance mode will have no effect on the control system. However, inthe actual magnetic disk apparatus, the shape of the main resonance modeitself varies due to manufacturing variation such as a machiningtolerance, and therefore the displacement of the magnetic head does notalways become 0. Thus, it is unavoidable that the magnetic head isdisplaced to a certain extent. In this case, the displacement directionof the magnetic head is sometimes the same as the displacement directionof the coil, which is an input point, and sometimes opposite to thedisplacement direction of the coil, because of individual differences ofthe carriage arm assemblies. This means that the observed displacementof the magnetic head varies between positive and negative, in otherwords, the phase in the main resonance mode with respect to the transfercharacteristic cannot be fixed in the positive or the negative, wherethe positive phase is defined as that the head is displaced in anopposite direction to a coil displaced direction, and the negative phaseis defined as that the head is displaced in the same direction with thecoil displaced direction.

A similar phenomenon occurs, even in one magnetic disk apparatus, due totemperature variation. Generally, a bearing used in the carriage of themagnetic disk apparatus is pressurized at a constant position in view ofthe manufacturing cost. If ambient temperature of the magnetic diskapparatus changes, the bearing section expands or contracts due to thetemperature variation which varies the amount of pressure on thebearing. Accordingly, the rigidity of the bearing section in the mainresonance mode is changed, so that the displacement of the bearingsection is fluctuated, in other words, the phase of the main resonancemode in the transfer characteristic cannot be defined as the positive orthe negative, as with the case of the manufacturing variation.

Inversion between the positive and the negative phases means that theoutput is inverted between the positive and the negative even if aconstant input is added. Thus, if providing a compensator forcontrolling negative phase vibration in the main resonance mode by meansof feedback control, positive phase of the main resonance mode becomesexcited by the feedback control system. Therefore, under a condition inwhich the phase of the main resonance mode is indeterminate as positiveor negative, it is difficult for the feedback control system to controlvibration of the main resonance mode.

For the above reason, it is difficult to achieve a magnetic diskapparatus described in JP-A-9-161430 specification, in which apparatusthe displacement of the magnetic head in the main resonance mode isdefined as 0.

On the other hand, in the method of using a tuned mass damper forcompensating the vibration of the carriage arm assembly, which vibrationis defined as residual vibration when positioning the head, there is aproblem that it is difficult to make an adjustment into the frequency ofthe target vibration mode. When high damping is not added by using thetuned mass damper, it is necessary to accurately adjust into thefrequency of the target vibration, and even if the adjustment deviatesfrom the target vibration slightly the effect wears off immediately.Further, even if using a material having a high damping effect in viewof the frequency variation, the vibration reduction effect will be alsoreduced.

In the case of using the high damping material, however, by directlyapplying the material to the residual vibration generating part, it ispossible to effectively reduce the amplitude of the residual vibration,and to improve convergence of the vibration, so that fine adjustmentcannot be omitted.

It is an object of the invention to solve the above problems byproviding a magnetic disk apparatus having improved recording densityand large recording capacity in which the servo band width is widenedfor improving positioning accuracy and for reducing positioning errors.

It is another object of the invention to provide a magnetic diskapparatus capable of reducing residual vibration generated by headpositioning operation, and improving the reading/writing speed, so thathigh speed transferring is achieved.

According to a first aspect of the invention, in order to solve theabove-described problems, there is provided a carriage arm assemblyincluding a carriage arm which includes a suspension fixing portion andtwo arm members disposed in quail-parallel to a disk surface, each ofwhich arm members has a coil side end area and a suspension side endarea which have smaller rigidity than that of a central area thereof.This feature makes the carriage arm to be easily deformable in the coilside end area and the suspension side end area, so that it possible toreduce displacement of a magnetic head in the main resonance mode.Further, this feature reduces influences of the main resonance mode onthe control system, widens a servo band width and increases recordingdensity. In order to make the coil side end area and the suspension sideend area of the arm member to have smaller rigidity than the centralarea, it may be also possible to make the widths of the coil side endarea and the suspension side end area of the arm member smaller thanthat of the central area thereof. Preferably, the width of the armmember is widen in the direction quasi-parallel to the surface of themagnetic disk in consideration of interference with the magnetic disk.However, it should be noted that it is also possible to widen the widthof the central area of the arm in the direction perpendicular to thesurface of the magnetic disk. Therefore, the present invention canadjust the mode displacement of the magnetic head in the main resonancemode by changing the shape of the arm member of the carriage arm.Moreover, since the phase is not inverted in the main resonance mode,the present invention is applicable to an actual disk apparatus.

However, it is also possible to construct the carriage arm in such a waythat the mode displacement of the magnetic head in the main resonancemode is adjusted so as to prevent the phase from inverting in the mainresonance mode, without the need for the above-configuration in whichthe coil side end area and the suspension side end area of the armmember have smaller rigidity than the central area of the arm member.

According to a second aspect of the invention, in solve theabove-described problems, there is provided a carriage arm assemblyhaving a carriage arm which includes a first arm member and a second armmember placed side by side in parallel to a disk surface, which armmembers are coupled with each other by using a damping material insertedtherebetween. In the vibration mode including in-plane bending of thearm, relative displacement takes place between the first arm member andsecond arm member, so that large distortion is caused in the dampingmaterial provided between the arm members, thereby it makes possible toenhance the damping effect of the damping material.

Furthermore, by making the rigidity of the central areas of the firstarm member and second arm member higher than that of the coil side endarea and suspension side end are, it is possible to further enhance thedamping effect. In the case of comparing the same head displacement inarm bending deformation, the rigidity of the end areas is relativelylow, so that no deformation occurs in the area of a large width in thecenter, and the deformation occurs at the end areas instead. Thisfeature increases relative displacement between the first arm member andsecond arm member, so as to produce greater distortion. Accordingly,this further enhances the damping effect of the damping material.

Further, by providing damping members on both ends of rigid membershaving higher rigidity than the damping material, more specifically onboth ends of a laminated material (hereinafter referred to as“restricting material”), and by putting this damping materials on planesquasi-parallel to the disk surface in the central area of the first armmember and the central area of the second arm member, it becomespossible to paste the damping material in the areas having a large widthin the center. This feature increases the area of the damping material,widens the area producing a damping effect, and can thereby furtherenhance the effect.

It is also possible to couple the first arm member the second arm memberonly via an elastic member without using a restricting member, in whichthe first arm member and the second arm member generate relativedisplacement therebetween so as to produce distortion in the elasticmaterial. This feature can produce a high damping effect. Thus, it ispossible to reduce the cost by eliminating the restricting material.

The features of the present invention have been described in the above.Other features of the present invention will become more apparent by thefollowing description of embodiments of the present invention.

Other objects, features and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a perspective view of a magnetic disk apparatus using acarriage arm assembly according to a first embodiment of the presentinvention;

FIG. 2 is a perspective view of the carriage arm assembly according tothe first embodiment of the present invention;

FIG. 3 is a top view of the carriage arm assembly according to the firstembodiment of the present invention;

FIG. 4 is a schematic view of the first embodiment of the presentinvention;

FIG. 5 is a drawing showing principles of operation of the firstembodiment of the present invention;

FIG. 6 is a finite element model of the first embodiment of the presentinvention;

FIG. 7 is a finite element analysis result in a main resonance mode ofthe first embodiment of the present invention;

FIG. 8 illustrates a transfer characteristic of the first embodiment ofthe present invention;

FIG. 9 is a top view of a carriage arm assembly according to a secondembodiment of the present invention;

FIG. 10 is a schematic view of the second embodiment of the presentinvention;

FIG. 11 is a drawing showing principles of operation of the secondembodiment of the present invention;

FIG. 12 is a finite element analysis result in a main resonance mode ofthe second embodiment of the present invention;

FIG. 13 illustrates a transfer characteristic of the second embodimentof the present invention;

FIG. 14 is a perspective view of a carriage arm assembly according to athird embodiment of the present invention;

FIG. 15 is a top view of the carriage arm assembly according to thethird embodiment of the present invention;

FIG. 16 is a side view of the carriage arm assembly according to thethird embodiment of the present invention;

FIG. 17 is a perspective view of the magnetic disk apparatus using thethird embodiment of the present invention;

FIG. 18 illustrates deformation of the third embodiment of the presentinvention;

FIG. 19 is a drawing showing a model of deformation principles of thethird embodiment of the present invention;

FIG. 20 is an enlarged view of the arm side of the third embodiment ofthe present invention;

FIGS. 21A and 21B are top views of a carriage arm assembly according toa fourth embodiment of the present invention;

FIG. 22 is a perspective view of a carriage arm assembly according to afifth embodiment of the present invention;

FIG. 23 is a perspective view of a carriage arm assembly according to asixth embodiment of the present invention;

FIG. 24 illustrates assembly of the carriage arm according to the sixthembodiment of the present invention;

FIG. 25 illustrates a transfer characteristic of the third embodiment ofthe present invention; and

FIGS. 26A and 26B illustrate positioning residual vibration waveforms ofthe third embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(Embodiment 1)

Referring to FIG. 1, FIG. 2 and FIG. 3, a slider 3 including a magnetichead (not shown) is mounted at the end of a carriage 1 via a suspension2. When a current flows through a coil 4, a force is generated between avoice coil motor 5 and the coil 4, so that the carriage 1 rotates arounda bearing section and thereby can position the slider 3 at an arbitraryradial position on a disk 6. The carriage 1 includes a carriage arm 7,and the carriage arm 7 has such a configuration in which the widths ofthe two arm members, corresponding to a front end area 8 and a back endarea 9, are smaller than the width of a central (intermediate) area 10.

FIG. 4 and FIG. 5 illustrate principles of operation of the presentinvention. In the examples in FIG. 1 to FIG. 3, since the widths of thefront end area 8 of the arm member and the back end area 9 of the armmember of the carriage arm 7 are smaller than the width of the centralarea 10 of the arm member, the present invention can be modeled so as tohave a 4-node link structure expressed with rigid sections 11 androtation sections 12 as shown in FIG. 4. Point A in FIG. 4 is a virtualposition of the magnetic head. Furthermore, a force acting on thecarriage arm 7 in a main resonance mode can be regarded as an inertialforce acting on the carriage arm 7 and is equivalent to a force input asshown in FIG. 4. When the force input shown in FIG. 4 is generated, thedeformation as shown in FIG. 5 occurs in view of a geometricrelationship of a rigid section 11, which can reduce the displacement ofpoint A showing the position of the magnetic head. This means that it ispossible to reduce mode displacement of the magnetic head in the mainresonance mode in the actual magnetic disk apparatus, and reduce theamplitude of the main resonance in the transfer characteristic.

Each section of the carriage arm 7 of the actual carriage is rigid, andnot rotation free, and therefore can be shown as the finite elementmodel shown in FIG. 6 used for an analysis to check the deformed shapein FIG. 5. FIG. 7 shows a deformed shape in the main resonance mode. Asshown in FIG. 7, the displacement at point C, which is the magnetichead, is smaller than the displacement at point B, which is the edge ofthe carriage arm 7, and the carriage arm 7 is deformed as shown in FIG.5. FIG. 8 shows a transfer characteristic, which is a displacement inthe direction of positioning the magnetic head when a unit force isinput (IN) to the coil section. The horizontal axis shows a frequency,the vertical axis shows a decibel value of displacement (mm), the solidline shows a transfer characteristic of the present invention and thenarrow line shows a transfer characteristic of a carriage according to aconventional system. From FIG. 8, it is clearly understandable that theamplitude in the main resonance mode is reduced compared to theconventional system.

As described above, the present invention can widen the servo band widthcompared to the conventional system. Furthermore, even if the shape ofthe main resonance mode changes due to manufacturing variation orvariation in the operating environment, the phase of the magnetic headis not inverted, and the present invention is therefore applicable tothe actual magnetic disk apparatus.

(Embodiment 2)

FIG. 9 is a top view of a carriage arm assembly according to a secondembodiment of the present invention. In the embodiment in FIG. 1 to FIG.3, the widths of the front end area 8 of the arm member and the back endarea 9 of the arm member of the carriage arm 7 are smaller than thewidth of the central area 10 of the arm member. On the other hand, inthe embodiment in FIG. 9, the width of each arm member of the entirecarriage arm 7 is reduced. This makes it possible to reduce the weightof the carriage arm, thus reduce inertial moment of the entire carriagearm assembly, which allows the time required for an access operation tobe shortened. FIG. 10 shows a drawing of principles of operation. In thecase of FIG. 10, the width of the entire carriage arm 7 is small, andtherefore the carriage arm assembly can be modeled as elastic beams 13instead of the rigid link mechanism as shown in FIG. 4. FIG. 11 shows acase where the carriage arm 7 is deformed. As with the case of FIG. 5,it is also understandable that this is the configuration with reduceddisplacement of the head.

FIG. 12 shows the shape of a main resonance mode which is analyzed usinga finite element analysis method, and FIG. 13 shows a transfercharacteristic. As with the case of FIG. 7 and FIG. 8, it is alsounderstandable in this case that the amplitude of the main resonancemode is small, while there is sufficient displacement so that the phasewill not be inverted.

As shown above, it is also possible to widen the servo band width in thesecond embodiment compared to the conventional system, and therefore itis possible to reduce positioning errors, and improve recording density,and at the same time, the phase of the magnetic head is not invertedeven if the shape of the main resonance mode changes due tomanufacturing variation and variation in the operating environment, andtherefore the present invention is applicable to an actual magnetic diskapparatus.

(Embodiment 3)

FIG. 14 is a perspective view of a carriage arm assembly according to athird embodiment of the present invention, and FIG. 15 is a top view ofthe carriage arm. FIG. 16 is a side view of the carriage arm.Furthermore, FIG. 17 shows an example of a magnetic disk apparatusincorporating the carriage arm assembly of the present invention. Aslider 53 including a magnetic head (not shown) is mounted at the end ofa carriage 51 via a suspension 52. When a current flows through a coil54, a force is generated between a voice coil motor 55 and the coil 54,the carriage 51 rotates centered on the bearing section 61 around arotation axis parallel to a rotation axis of the disk, and can therebyposition the slider 53 at an arbitrary radial position (target track) ona disk 56.

The carriage 51 is the same as that of the first embodiment in which thecarriage arm members 57 a and 57 b have a configuration such that thewidths of the arm front end areas 58 a and 58 b and the arm back endareas 59 a and 59 b have widths smaller than the widths of the armcentral areas 60 a and 60 b.

Here, with respect to subscripts “a” and “b” in FIG. 15, the right sidein the direction seen from the body 61 to the suspension fixing portion12 is expressed with subscript “a”, and the left side is expressed withsubscript “b”. For example, 58 a is a front end of the arm member 57 a.The arm members 57 a and 57 b are provided within a plane parallel tothe disk surface.

A restricting plate (restricting member) 64 is pasted to the planes ofthe arm central areas 60 a and 60 b so as to be parallel to the disksurface just like a bridge through a damping member 63, that is, the armcentral areas 60 a and 60 b are connected through the damping member 63.Here, a high polymer material having viscoelasticity (hereinafterreferred to as “viscoelastic body”) is used as the damping member 63.This is because the damping member 63 itself has adhesiveness and it caneasily be pasted to the arm members and is convenient for assembly. Ofcourse, the damping member 63 can be substituted by a member having ahigh damping effect such as rubber. In this example, the restrictingplate 64 is a stainless steel plate of 50 to 200 μm thick, and thevisco-elastic body 63 is an adhesive material of 50 to 100 μm thick andalso serves as a member supporting the restricting plate 64 onto thecentral areas 60 a and 60 b. The restricting plate (restrictingmaterial) 64 is made of a rigid material having higher rigidity than thevisco-elastic body 63 (however, different from rigid sections 65).

FIG. 18 illustrates a deformed shape of the carriage arm assembly in themain resonance mode. Since the widths of the arm front end areas 58 aand 58 b and arm back end areas 59 a and 59 b are smaller than thewidths of the arm central areas 60 a and 60 b, as shown in the arm shapein FIG. 15, the carriage arm assembly can therefore be modeled with a4-node link structure virtually expressed with rigid sections 65 androtation sections 66 as shown in FIG. 19. At this time, the centralareas 60 a and 60 b corresponding to the rigid sections 65 move so as torotate around the back end area 59 a or 59 b as fulcrums, so thatrelative displacement is produced as indicated by arrows 67 in FIG. 18.At this time, since the restricting plate 64 has sufficient rigidity,the length is invariable, so that shear strain in the viscoelastic body63 is produced in the in-plane direction. The visco-elastic body 63converts this distortion energy to thermal energy, and therebydissipates it so as to produce a damping effect. According to thismechanism, if the distortion of the viscoelastic body 63 is large, thatis, the greater the relative displacement between the restricting plate64 and the central areas 60 a and 60 b of the respective arm members,the greater the energy consumed, enhancing the damping effect.Furthermore, it is understandable that the greater the area of thevisco-elastic body 63 pasted to the central areas 60 a and 60 b of thearm members, the more energy is consumed in more parts so as to enhancethe damping effect.

Increasing the servo band width requires to increase the frequency inthe main resonance mode, which is a primary vibration mode of thecarriage, or to reduce a gain in a transfer characteristic in which theforce generated in the coil is defined as an input, and the displacementof the magnetic head in the positioning direction is defined as anoutput. FIG. 25 shows an effect of the present invention with respect tothe transfer characteristic. Compared to the transfer characteristic 79when the present invention is not used, the gain in the main resonancemode reduces with the transfer characteristic 80 when the presentinvention is used. Furthermore, FIGS. 26A and 26B show a signal ofdeviation from a target track when the head comes close to the targettrack during a positioning operation. FIG. 26A shows a waveform in acase where the present invention is not used, and FIG. 26B shows awaveform in a case where the present invention is used. It isunderstandable that the frequency and amplitude with a high frequencyindicated by an arrow 81 is reduced.

As shown in FIG. 16, this embodiment adopts a configuration whereby therestricting plates 64 are pasted to all arms through the viscoelasticbodies 63. This makes it possible to obtain a damping effect duringbending and deformation of all the arms. However, in the case of thecarriage of which all the arms coupled with the body 61, the vibrationmode involving in-plane bending of the arm represented by the mainresonance mode is the vibration mode in which the entire carriage isdeformed as one structure and even if a section of producing a dampingeffect is provided partially, the damping ratio with respect to thevibration mode in the carriage as the entire system increases, andtherefore vibration of all the arms can also be reduced.

Accordingly, by pasting the restricting plates 64 and viscoelasticbodies 63 only to the outside arms 69 without pasting the restrictingplates 64 and viscoelastic bodies 63 to all the arms 68 in theintermediate area shown in FIG. 16, it is possible to give a dampingeffect against vibration of all the arms. This means that, in the actualmagnetic disk apparatus, by pasting the restricting plates 64 to thearms 69 at both ends of the carriage arm using visco-elastic bodies 63,it becomes possible to reduce deterioration of the gain in the vibrationmode involving the in-plane bending of the arm in the transfercharacteristic at all the magnetic heads. Thus, by avoiding pasting therestricting plates 64 to the arms 68 in the intermediate section, it canbe possible to reduce the number of pasting locations and thereby reduceassembly man-hours.

In the height direction within the magnetic disk apparatus, a pluralityof intermediate section arms 68 alternate with a plurality of disks 56.Therefore, there are often dimensional restrictions in the thicknessdirection of the arms. In such a case, by providing a groove 70 in thethickness direction as shown in FIG. 20 and pasting the restrictingplate 64 inside through the viscoelastic body 63, it is possible toavoid increase in size in the thickness direction. In this case, byproviding the groove 70, reduction of rigidity of the arm may be caused,however when considering in contrast to bending rigidity of beams, thethickness of the arm member only has a proportional influence on therigidity in the in-plane direction of the arm, and therefore thereduction of rigidity is relatively small compared to the influence bythe width of the arm member having a cubic influence in the in-planedirection. Especially in the case of this embodiment, since the placewhere the restricting plate 64 is pasted is the central areas 60 a and60 b of the arm members widened so as to be regarded as a rigid body,the influence of the groove 70 on bending deformation of the arm membersis very small.

Furthermore, with respect to bending rigidity in the out-of-planedirection of the arm, though the visco-elastic body 63 is inserted, thehigh rigidity restricting plate 64 is attached outside, so that it ispossible to considerably reduce deterioration of the rigidity in theout-of-plane direction by providing the groove 70. Furthermore, whendistortion concentration on the groove 70 is considered, the distortionoccurs in the visco-elastic body 63 and it is also possible to achievethe effect of attenuating the out-of-plane vibration of the arm.

When the restricting plate 64 is pasted to the central areas 60 a or 60b of the arm member in the assembly process, it is desirable to pastethe visco-elastic body 63 only to the areas where the restricting plate64 faces the central area 60 a or 60 b. This is because even if thevisco-elastic body 63 is placed in the exposed area in the space betweenthe central areas 60 a and 60 b of both arm members of the planes facingthe arms of the restricting plate 64, and if the rigidity of therestricting plate 64 is sufficient, no distortion is generated in thevisco-elastic body 63, and therefore no damping effect is expectedthereby. Furthermore, if a large part of the visco-elastic body 63 isexposed, a part of the viscoelastic body 63 may be peeled off and mayconvert to dust particles on a microscopic scale. This feature also hasthe effect of avoiding those. Another method of solving this problem isto paste an additional restricting plate to the visco-elastic body 63exposed in the space between the central areas 60 a and 60 b of this armmember. This provides an advantage of improving the rigidity of therestricting plate 64.

(Embodiment 4)

FIG. 21A and FIG. 21B show a fourth embodiment of the present invention.As shown in FIG. 21A, the widths of the arm members 57 a and 57 b of thecarriage arm are constant, and the dimensions such as the thickness,length and rigidity, etc. of the arm members 57 a and 57 b are designedso as to produce an arm deformation as shown in FIG. 21B. In this case,also, a relative displacement occurs near the intermediate area of thearm members 57 a and 57 b, and therefore distortion occurs in theviscoelastic body 63 below the restricting plate 64, so that theabove-described mechanism makes it possible to achieve a damping effect,which makes the arm members 57 a and 57 b gradually bendable over theentire area of the arm members, which makes the relative displacementnear the central area smaller than that of the third embodiment andreduces the damping effect. Furthermore, by increasing the width of thearm members to increase the area to which the viscoelastic body 63 ispasted, the bending rigidity of the arm members increases, so that theamount of deformation is reduced and thereby the damping effect isreduced, however when overall rigidity of the arm member 57 increases,the resonance frequency in vibration mode involving in-lane bending ofthe arm including the main resonance mode can be increased.

(Embodiment 5)

FIG. 22 shows a fifth embodiment of the present invention. As with thecase of the third embodiment, the shape of the carriage arm has aconfiguration that the widths of the front end areas 58 a and 58 b andthe arm back end areas 59 a and 59 b of the arm members 57 a and 57 b ofthe carriage arm are smaller than the widths of the central areas 60 aand 60 b of the arm members. Furthermore, a restricting member 71, whoseenlarged view is shown in the figure, is inserted between the centralareas 60 a and 60 b using two viscoelastic bodies 63. As with the caseof the third embodiment, this produces distortion in the viscoelasticbody 63 under the restricting member 71 with respect to relativedisplacement of the central areas 60 a and 60 b of the arm member, so asto generate a damping effect. In this case, by making the thickness ofthe restricting plate 71 equivalent to that of the arm, the dimensionalincrease in the out-of-plane direction of the arm can be suppressed.Furthermore, even if the restricting plate 71 is pasted to all the armsor pasted to some arms, the aspect that the damping effect can beexpected for all the arms is the same as the case of the thirdembodiment.

(Embodiment 6)

FIG. 23 shows a sixth embodiment. As shown in the case of the third andfifth embodiments, the carriage arm has a configuration in which thewidths of the front end areas 58 a and 58 b and the back end areas 59 aand 59 b of the arm members 57 a and 57 b of the carriage arm aresmaller than the widths of the central areas 60 a and 60 b. Here, thecarriage has a configuration in which a thermoplastic damping material72 is inserted along the shape of the central areas 60 a and 60 b of thearm members. For the damping material 72, it is desirable to mix avisco-elastic body with a high damping effect with thermoplastic resinand shape it or use an elastic material with a high damping effect suchas rubber. This embodiment has no restricting material, contrary to thecase of the third to fifth embodiments, however the central areas 60 aand 60 b of the arm members have dual functions of the restrictingmaterials to produce distortion in the damping material 72 when relativedisplacement occurs, and can thereby generate a damping effect similarto that explained so far. Such a configuration eliminates the need for arestricting material and simplifies the structure.

FIG. 24 shows an assembling method according to the sixth embodiment. Ina state “A” before the suspension 52 is attached, a horizontal mold 73is inserted between the arms in the in-plane direction. Furthermore, thevertical mold 74 is inserted from the outside of the plane in a state“B”. The vertical mold 74 is provided with cylinders 75 and 76 whoseexternal shape is determined according to the holes perforated betweenthe arm members 57 a and 57 b, and tubes 77 are provided on the centralaxis line. Furthermore, nozzles 78 are provided on sides of thecylinders 76 and 77 corresponding to the arm positions. In the state“B”, a space surrounded by the horizontal mold 73 and vertical mold 74is formed between the central areas 10 a and 10 b of the arm member. Inthis state, a damping material melted at a high temperature is extrudedand molded into the above-described space from one side of the tube 77through the nozzles 78, cooled down, and hardened after a predeterminedtime, so that the damping material 72 is molded in this way. In theabove process, the damping material 72 is molded near the center of thearm member. FIG. 23 shows a flat plane as the planes of the arm membercentral areas 60 a and 60 b facing the damping section 72, however theplane is not limited to a flat plane, and it is further desirable toprovide projections and depressions to increase the area of contact withthe damping material 72. The assembly process shown in FIG. 24 allowsthe damping material 72 to be molded simultaneously for all arms, andtherefore it is effective to provide the damping material 72 for allarms, however, of course, it is also possible to give the dampingmaterial 72 only to some arm members as in the cases of the foregoingembodiments.

By using the carriages according to the third to sixth embodiments ofthe present invention, it is possible to achieve high damping effectsfor various vibration modes involving in-plane bending of arms.Especially, it is possible to widen the servo band width and improve thepositioning accuracy by reducing the gain in the transfer function inthe main resonance mode and provide a magnetic disk apparatus with highrecording density. Furthermore, it is possible to reduce residualvibration during an operation of positioning the head in the targetmode, improve the reading/writing speed, and provide a magnetic diskapparatus with high-speed transfer capability.

In the above-described explanations, “arm in-plane bending primary mode”refers to a mode of deforming each of a plurality of arm members justlike primary bending of a cantilever, and refers to the same vibrationmode as the “end arm mode” in the above-described literature “ActiveDamping in HDD Actuator”. Furthermore, the “in-plane direction” meansthe direction along the plane parallel to the disk plane, and the“out-of-plane direction” means the axial line direction perpendicular tothe disk plane. Furthermore, the vertical/horizontal ratio and thedimensional ratio among different sections in the drawings used forconvenience of explanation in the explanations do not necessarilyreflect correct values.

The present invention can reduce the displacement of the magnetic headin the main resonance mode, and prevents the phase of the magnetic headfrom inverting in the case that machining tolerance and ambienttemperature change, and can thereby implement a magnetic disk apparatuscapable of improving its recording density and having large recordingcapacity by widening the servo band width, improving the positioningaccuracy, and reducing positioning errors.

Furthermore, the present invention can give a high damping effect tovarious vibration modes accompanied by in-plane bending of the arm,reduce vibration of the carriage, and reduce positioning errors, and canthereby provide a magnetic disk apparatus with high recording density.The present invention can also provide a magnetic disk apparatusallowing high-speed transfers by reducing residual vibration during ahead positioning operation, and improving the reading/writing speed.

It should be further understood by those skilled in the art that theforegoing description has been made on embodiments of the invention andthat various changes and modifications may be made in the inventionwithout departing from the spirit of the invention and the scope of theappended claims.

1. A carriage arm assembly for swingably supporting a magnetic head,comprising: a slider on which the magnetic head is mounted; a suspensioncarrying the slider; a carriage arm to which the suspension is attached;and a body section provided at a base end of the carriage arm, whichbody section extends so as to completely surround a rotational axis, adistal side portion of the body section being disposed at a positionbetween the rotational axis and the magnetic head and substantially awayfrom the rotational axis in a direction toward the magnetic head, thecarriage arm including first and second arm members extending from thedistal side portion of the body section and being substantially inparallel with a swinging plane of the carriage arm, and a fixing portionprovided at a distal end of the carriage arm for mounting the suspensionthereon, and each of the first and second arm members comprise narrowsections in a distal end area and a base end area thereof, a width ofthe narrow sections in a swinging direction being smaller than a widthof an intermediate area of the first and second arm members, so that thecarriage arm assembly is easily deformed in the distal and base endareas of the first and second arm members.
 2. The carriage arm assemblyaccording to claim 1, wherein first and second arm members and saidfixing portion are integrated to form said carriage arm.
 3. The carriagearm assembly according to claim 1, wherein the first and second armmembers are coupled with each other in the intermediate areas thereof bymeans of a coupling member comprising a damping member.
 4. The carriagearm assembly according to claim 1, wherein, in a main resonance modecorresponding to a primary vibration mode in an approximate positioningdirection, magnetic head is displaced in a direction same with that ofthe fixing portion of the carriage arm, the amount of displacement ofthe magnetic head being smaller than that of the fixing portion.
 5. Thecarriage arm assembly according to claim 4, wherein the amount ofdisplacement of the magnetic head is greater than 0.